A wide variety of petroleum-degrading microorganisms has been found to bring about the formation of oil-in-water emulsions while growing on hydrocarbons. These emulsions are microbiological in origin and appear to be mediated either by the cells themselves or by the production of extracellular emulsifying agents. For example, the growth of Mycobacterium rhodochrous NCIB 9905 on n-decane yields an emulsifying factor which was reported by R. S. Holdom et al. [J. Appl. Bateriol., 32, 448 (1969)] to be a nonionic detergent. J. Iguchi et al. [Agric Biol. Chem., 33, 1657 (1969)] found that Candida petrophilium produced an emulsifying agent composed of peptides and fatty acid moieties, while T. Suzuki et al. [Agric. Biol. Chem., 33, 1619 (1969)] found trehalose lipid in the oil phase of culture broths of various strains of Arthrobacter, Brevibacterium, Corynebacterium and Norcardia.
Torulopsis gropengiesseri was found to produce a sophorose lipid, while rhamnolipids are reported by K. Hisatsuka et al. [Agric. Biol. Chem., 35, 686 (1971)] to have been produced by Pseudomonas aeruginosa strain S7B1 and by S. Itoh et al. [Agric. Biol. Chem., 36, 2233 (1971)] to have been produced by another P. aeruginosa strain, KY4025. The growth of Corynebacterium hydrocarbolastus on kerosene was reported by J. E. Zajic and his associates [Dev. Ind. Microbiol., 12, 87 (1971); Biotechnol. Bioeng., 14, 331 (1972); Chemosphere, 1, 51 (1972); Crit. Rev. Microbiol., 5, 39 (1976); U.S. Pat. No. 3,997,398] to produce an extracellular heteropolysaccharide which, among other properties, emulsified kerosene, Bunker C fuel oil and other fuel oils.
In U.S. Pat. No. 3,941,692, we described the use of an Arthrobacter species, RAG-1 (which, upon deposit with the American Type Culture Collection, has been designated as Arthrobacter Sp. ATCC 31012 and is now known to have been an Acinetobacter species and has been redesignated as Acinetobacter Sp. ATCC 31012) to clean oil-contaminated tank compartments by allowing the organism to aerobically grow on the oily wastes in such tanks using sea water containing added nutrients. During that microbially-induced cleaning process, the organism appeared to secrete one or more dispersants during the fermentation, since the cell-free fermentation medium was also effective in cleaning waste oil from such tanks.
Further studies on the microbial degradation of crude oil by this organism [Appl Microbial., 24, 363 (1972); Appl. Microbiol., 30, 10 (1975)], showed that RAG-1 emulsified the oil during exponential growth, probably by producing an extracellular emulsifying agent which acted to break up the oil droplets into smaller units and thereby produce new surface area, necessary for the increasing cell population. At the 1st International Congress for Bacteriology held Sept. 2-7, 1973 [Int. Assoc. Microbial, Soc. Abstracts, Vol. II, p. 201], we reported that this extracellular emulsifying agent had been partially purified from stationary phase cultures of RAG-1 growing on 0.4% hexadecane, 0.075 M urea and 5.8 mM dibasic potassium phosphate in sea water. The partially purified extracellular emulsifying agent was obtained by extensively dialyzing and then lyophilizing the cell-free fermentation broth, yielding 0.25 mg per ml of culture fluid of a dry powder which was capable of forming a stable oil-in-water emulsion with 40 times its weight of crude oil.
Notwithstanding the many publications on the subject, however, microbially-induced emulsification of oil is poorly understood from both mechanistic and teleological points of view. Microorganisms can utilize crude oil as a substrate for growth with or without concomitant oil emulsification. Where emulsification has occurred because of the production of extracellular emulsifying agents, in general the preparations have not been purified sufficiently to identify the active components. In sum, none of these extracellular bioemulsifiers has been well characterized and very little is known about their chemical properties, mode of action or biological function.